I am fairly new to the world of 3D printing, and I would like to get a better understanding of why one needs the top cover/ lid of the 3D printer. What is it generally good for? Is it to avoid potentially toxic fumes evaporating and poisoning the surrounding air, is it to keep the temperature in the printer higher, etc.?

More concrete, I wondered about a sticker on the top cover saying "Just when printing PLA, no need to use this top cover".

I read about PLA having the need to cool down quickly in order to achieve a better print quality. Consequently, it would be better to leave the top cover off, while printing with PLA. However, the sticker suggests otherwise. I read that some leave the door open, when printing with PLA, but have the top cover on, which in any case seems arbitrary to me. Another info i gathered is that ABS likes it rather hot (I have yet to print with it so I would not know), and therefore people like to keep the top cover on when printing with ABS.

Can somebody give a quick overview on the different reasons on why to use or not use the top cover? I would highly appreciate it.

Timon,Your understanding about heat retention is correct. Some materials, such as ABS, benefit from a higher enclosure temperature (top on, door closed). Some, such as PLA, work better when cooled quickly (top off and/or door open). The confusion arises from the poor punctuation on the stick-on label; remove the comma and it makes a little more sense although rewording to "No need to use this cover when printing PLA" would have been far better.

Regarding fume containment; fumes will be generated with or without the cover. The cover may make you think the fumes are "contained" but they will ultimately end up in your work space. I modified my printer with an exhaust port venting to the outdoors.

... and there I thought I'd know English Thank you very much for the explanation. I wish I would have had this information weeks ago. My understanding of it was exactly the other way round, as in: I am looking at the cover and read "Just when printing PLA!" and then the comma as in "otherwise", "no need to use this cover". Now that I know it does compute though.